Belt type infinite variable-speed drive

ABSTRACT

A belt type infinite variable-speed drive using a ball screw is proposed which is compact and noise-free. The nut of the ball screw mechanism is fixed to a casing and the threaded shaft is rotatably coupled to a movable pulley member through a ball bearing so that ball circulating portions on the nut will not rotate while the movable pulley member is movable axially. Also, the ball circulating portions, which are low in the load bearing capacity, are oriented in such a direction that load hardly acts on the ball screw mechanism. This makes it possible to compactly and rationally design a belt type infinite variable-speed drive and to suppress noise due to vibration of the balls in the ball circulating portions.

BACKGROUND OF THE INVENTION

[0001] This invention relates to a belt type infinite variable-speed drive having a movable pulley portion moved axially by a ball-screw mechanism.

[0002] A belt type infinite variable-speed drive has a fixed pulley portion and a movable pulley portion around which is wound a transmission belt. They are mounted on a rotary shaft with their belt-receiving surfaces opposing each other. By axially moving the movable pulley portion by means of a direct acting actuator, the winding diameter of the transmission belt is changed in a stepless manner. As direct acting actuators, there are hydraulic ones and mechanical ones such as ball-screw mechanisms.

[0003] In a ball-screw mechanism, a nut having helical thread grooves formed in its inner periphery is mounted on a threaded shaft having helical thread grooves formed in its outer periphery. Between the opposed thread grooves of the threaded shaft and the nut, a plurality of balls are rollably received so that the threaded shaft and the nut can smoothly move axially relative to each other. The nut has ball circulating portions for infinitely circulating the balls between the thread grooves. Many of such ball-screw mechanisms are of a type in which by axially moving the nut with the axial movement of the threaded shaft prevented and the nut moved relative to the threaded shaft, a moving member coupled to the nut is linearly moved.

[0004] Since belt type infinite variable-speed drives using a ball screw mechanism as a direct acting actuator makes more compact design possible than ones using a hydraulic actuator, they are used as infinite variable-speed drives for e.g. automobiles in which the mounting space is limited, particularly small cars.

[0005] A prior art belt type infinite variable-speed drive is described in JP patent publication 8-33170. In this belt type infinite variable-speed drive, by turning the nut with the threaded shaft of the ball screw rotatably and axially movably supported to a support member provided integrally with a casing, a movable pulley portion as a movable member coupled to the nut is linearly moved in the axial direction.

[0006] Since a belt type infinite variable-speed drive using the above-described conventional ball screw mechanism is of a type in which the nut is turned, the circumferential positions of the ball circulating portions provided on the nut change with the rotation of the nut. Since there is a clearance between the ball circulating portions and the balls to smoothly circulate the balls, the balls in the ball circulating portions cannot bear loads such as moment loads and radial loads that act on the ball screw mechanism. Also, the directions of the loads that act on the ball screw mechanism of the belt type infinite variable-speed drive are substantially constant.

[0007] In a conventional belt type infinite variable-speed drive in which the nut turns, the portions where the ball circulating portions are provided, which are low in the resistance to load, are periodically oriented in the load direction. Thus, it is necessary to additionally increase the rigidity of the ball screw mechanism, so that no rational design is possible. Thus, further compactness of the belt type infinite variable-speed drive is impossible.

[0008] Also, since there is a clearance between the ball circulating portions and the nut, when the ball circulating portions turn together with the nut, the balls vibrate and collide against the walls of the ball circulating portions. This produces noise and wears the balls and the walls of the ball circulating portions.

[0009] An object of this invention is to provide a belt type infinite variable-speed drive of compact and rational design using a ball screw mechanism and to lessen noise.

SUMMARY OF THE INVENTION

[0010] According to this invention, there is provided a belt type infinite variable-speed drive comprising a fixed pulley member and a movable pulley member around which is wound a transmission belt and which are mounted on a rotary shaft with their belt-receiving surfaces facing each other, a ball screw mechanism for moving the movable pulley member axially to change the winding diameter of the transmission belt in a stepless manner, the ball screw mechanism comprising a threaded shaft formed with a helical thread groove in outer periphery thereof, a nut formed with a helical thread groove in inner periphery thereof and mounted on the threaded shaft, the threaded shaft being axially movable relative to the nut, and a plurality of balls rollably received between the opposed thread grooves of the threaded shaft and the nut, a ball circulating portion provided in the nut for infinitely circulating the balls between the thread grooves, the movable pulley member being moved axially by driving the threaded shaft with the nut arranged so as to be not rotatable and not axially movable and the threaded shaft coupled to the movable pulley member so as to be rotatable and axially movable.

[0011] That is, by coupling the ball screw mechanism to the movable pulley member with the nut unrotatable and not axially movable and the threaded shaft rotatable and axially movable, the ball circulating portions of the nut are prevented from turning when the movable pulley member is axially moved. The ball circulating portions, which are low in the load bearing capacity, are oriented in such a direction that loads will not act on the ball screw mechanism to make compact and rational design possible and to prevent noise due to vibration of the balls in the ball circulating portions.

[0012] By arranging the ball circulating portions within the outer diameter of the nut, it is possible to narrow the space on the outer peripheral side of the nut and make compact the diametrical dimension of the belt type infinite variable-speed drive. As the ball circulating portions disposed within the outer diameter of the nut, internal ball deflector type or guide plate type ones can be used.

[0013] Even if the ball circulating portions are provided in a plurality of numbers, by arranging them in an area where the load acting on the ball screw mechanism is small, it is possible to make design of the belt type infinite variable-speed drive compact and rational.

[0014] By forming the threaded shaft hollow, it is possible to couple its inner peripheral side to the movable pulley member through a bearing so as to be rotatable.

[0015] In an arrangement in which a coupling member comprising a flange extending outwardly beyond the outer periphery of the threaded shaft and an overhang overhanging along the outer periphery of the nut outwardly from the flange to form an annular space for receiving the nut between the overhang and the outer periphery of the threaded shaft, and a gear for transmitting a driving force to the threaded shaft is provided on the outer periphery of the overhang, it is possible to increase the effective length of the threaded shaft and shorten its overall length to shorten the axial dimension of the belt type infinite variable-speed drive.

[0016] By forming the gear integrally with the coupling member, it is possible to reduce the number of parts.

[0017] By making the overhanging length of the overhang larger than the maximum stroke of the axial relative movement between the threaded shaft and the nut to cover the outer peripheral side of the annular space over the entire axial length, it is possible to prevent scattering of lubricant for the ball screw mechanism as the threaded shaft turns. If grease scatters outwardly, it may stick to the transmission belt, thereby lowering the frictional force between the belt and the pulley.

[0018] By providing a sealing means for sealing the annular space between the inner periphery of the overhang and the outer periphery of the nut, it is possible to more reliably prevent scattering of the lubricant.

[0019] As the seal means, setting the radial gap between the inner periphery of the overhang and the outer periphery of the nut may be set at a small value, or an elastic member to the inner periphery of the overhang and the outer periphery of the nut to seal the radial gap therebetween.

[0020] Other features and objects of the present invention will become apparent from the following description made with reference to the accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

[0021]FIG. 1 is a longitudinal sectional view showing a belt type infinite variable-speed drive of a first embodiment;

[0022]FIG. 2 is a similar view showing the movable pulley member which has moved;

[0023]FIG. 3A is a cutaway perspective view of the nut of FIG. 1;

[0024]FIG. 3B is a similar view of a modified embodiment of the nut;

[0025]FIGS. 4A and 4B are partially omitted longitudinal sectional views of a second embodiment; and

[0026]FIG. 5 is a similar view of a third embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0027] The embodiments of this invention will be described with reference to FIGS. 1-5. FIGS. 1-3 show the first embodiment. As shown in FIG. 1, in this belt type infinite variable-speed drive, a fixed pulley member 2 and a movable pulley member 3 around which is wound a transmission belt 1 are mounted on a rotary shaft 4 with their belt-receiving surfaces 2 a, 3 a facing each other. By axially moving the movable pulley member 3 by means of a ball thread mechanism 5, the winding diameter of the transmission belt 1 is changed in a stepless manner.

[0028] The fixed pulley member 2 is provided with a tubular portion 6 extending toward the movable pulley member 3 and is coupled through a key to the rotary shaft 4 so as to rotate together. The rotary shaft 4 has its movable pulley member side supported on a casing 8 by a ball bearing 7 mounted on the tip of the tubular portion 6. Although not shown, the fixed pulley member 2, too, is supported on a casing by a bearing.

[0029] The movable pulley member 3 has a tubular portion 9 on the backside of the belt-receiving surface 3 a, and is coupled to the tubular portion 6 of the fixed pulley member 2 through a slide key 10 so as not to rotate together but to be slidable in the axial direction.

[0030] The ball-screw mechanism 5 comprises a threaded shaft 11 formed with a helical thread groove on its outer periphery, a nut 12 formed with a helical thread groove in its inner periphery and mounted on the threaded shaft 11 so as to be movable in the axial direction relative to the threaded shaft 11, and a plurality of balls 13 rollably received between the thread grooves 11 a and 12 a. The threaded shaft 11 is in the shape of a hollow tube and has its inner periphery rotatably supported on the tubular portion 9 of the movable pulley member 3 by a ball bearing 14. The nut 12 is fitted in the inner periphery 8 a of a recess of the casing 8 so that its rotation and axial movement are impossible.

[0031] The threaded shaft 11 is provided with a small-diameter portion 15 at its end on the side of the movable pulley member 3. An annular coupling member 18 having a flange 16 and an overhang 17 extending from the flange 16 along the outer periphery of the nut 12 is mounted on the small-diameter portion 15. In order to rigidly mount the coupling member 18, the small-diameter portion 15 is knurled.

[0032] On the outer periphery of the overhang 17, a gear 20 is mounted which slidably meshes with a gear 19 rotated by a motor (not shown). The threaded shaft 11 is rotated through the gear 20 and the coupling member 18. In order to smoothly slide the gear 20 relative to the gear 19, the gear 20 is formed of a resin that is low in friction coefficient.

[0033] The coupling member 18 is formed by pressing which is a combination of drawing and burring of a steel plate. The height of the flange 16 is set slightly higher than the nut 12 so that the latter can be housed in an annular space 21 formed between the outer periphery of the threaded shaft 11 and the inner periphery of the overhang 17.

[0034] By driving the gear 19 with a motor, the threaded shaft 11, which is rotatably supported by the ball bearing 14, moves in the axial direction relative to the fixed nut 12 while rotating around the movable pulley member 3, thereby pushing and sliding the movable pulley member 3 toward the fixed pulley member 2. Thus, the distance between the belt receiving surface 3 a of the movable pulley member 3 and the opposed belt receiving surface 2 a of the fixed pulley member 2 will narrow, so that the winding diameter of the transmission belt 1 increases.

[0035] Thus, in order to increase the winding diameter of the transmission belt 1, it is necessary to push up the transmission belt with the belt receiving surfaces 2 a and 3 a. Therefore the pushing force of the threaded shaft 11 has to be large. Thus, the end faces of the outer ring and the inner ring of the ball bearing 14, on which the pushing force of the threaded shaft 11 acts, are fixed by a snap ring 22 and a shoulder 23 of the tubular portion 9.

[0036] Conversely, when the winding diameter of the transmission belt 1 decreases, the pushing-down force from the transmission belt acts on the belt receiving surfaces 2 a and 3 a, so that it is possible to slide the movable pulley member 3 in the opposite direction by means of the threaded shaft 11 with a small pulling force. Thus, it is not particularly necessary to fix the end faces of the inner and outer rings of the ball bearing 14 at their opposite ends to the snap ring 22 and the shoulder 23.

[0037]FIG. 2 shows a state in which the stroke of the axial relative movement of the threaded shaft 11 and the nut 12 is maximum. At this time, the tip of the overhang 17 laps over the tip of the nut 12. The radial gap between the inner periphery of the overhang 17 and the outer periphery of the nut 12 is set small enough to seal the annular space 21. Thus, grease as a lubricant for the ball screw mechanism 5 will not splash out.

[0038]FIG. 3A shows the interior of the nut 12 by partially cutting out. As described above, the helical groove 12 a is formed in the inner peripheral surface of the nut 12. In order to infinitely circulate the balls 13, ball circulating portions 12 b which couple the adjacent grooves 12 a together are provided. The ball circulating portions 12 b are of an internal ball deflector type and circulate the balls 13 for every turn of the grooves 12 a. The nut 12 of FIG. 3a has two ball circulating portions 12 b arranged opposite to each other spaced 180°. It is fitted in the inner diameter 8 a of the recess of the casing 8 with the ball circulating portions 12 b directed in a horizontal direction, in which no load acts on the ball screw mechanism 5.

[0039]FIGS. 3B shows a modified embodiment of the nut in which two ball circulating portions 12 b are put together in a phase in a single direction.

[0040] Each ball circulating portion 12 b is provided so as to be received within the outer diameter of the nut 12. In order to smoothly circulate the balls 13, a clearance is provided between the balls 13 and the ball circulating portion 12 b. Since the nut 12 is used so as not to rotate while the balls 13 are circulating, they will not collide against the wall of each ball circulating portion 12 b.

[0041]FIGS. 4A and 4B show the second embodiment. This belt type infinite variable-speed drive has the same basic structure as the first embodiment, and differs only in the form of the overhang 17 of the coupling member 18. The overhang 17 overhangs with a small gap formed between it and the outer periphery of the nut 12, and a rubber seal member 24 is provided on the inner periphery thereof at its tip to seal the gap. Thus, in this embodiment, too, the annular space 21 is sealed, so that lubricating grease for the ball screw mechanism will not splash out.

[0042]FIG. 5 shows the third embodiment. This belt type infinite variable-speed drive is basically the same in its basic structure as the first embodiment, and differs only in that the coupling member 18 is formed integral with the gear 20 by injection-molding a resin. Other portions in the second and third embodiments are the same as in the first embodiment. Thus they are shown by the same numerals as in FIGS. 1 and 2.

[0043] In each of the embodiments, the coupling member 18 is fitted on the outer periphery of the threaded shaft 11 at its end. But it has only to be reliably secured to the end of the threaded shaft 11. Thus, it may be secured to the end face or to the inner periphery of the threaded shaft 11.

[0044] As described above, with the belt type infinite variable-speed drive of this invention, by mounting the nut of the ball screw mechanism so as to be not rotatable and not axially movable and coupling the threaded shaft to the movable pulley member so as to be rotatable and axially movable, when the movable pulley member is axially moved, the ball circulating portions of the nut do not rotate. Also, the ball circulating portions, which are low in the resistance to load, are directed in such a direction that no load acts on the ball screw mechanism. Thus, it can be designed compactly and rationally. Also, it is possible to prevent noise due to vibration of the balls in the ball circulating portions. 

What is claimed is:
 1. A belt type infinite variable-speed drive comprising a fixed pulley member and a movable pulley member around which is wound a transmission belt and which are mounted on a rotary shaft with their belt-receiving surfaces facing each other, a ball screw mechanism for moving said movable pulley member axially to change the winding diameter of said transmission belt in a stepless manner, said ball screw mechanism comprising a threaded shaft formed with a helical thread groove in outer periphery thereof, a nut formed with a helical thread groove in inner periphery thereof and mounted on said threaded shaft, said threaded shaft being axially movable relative to said nut, and a plurality of balls rollably received between the opposed thread grooves of said threaded shaft and said nut, a ball circulating portion provided in said nut for infinitely circulating said balls between said thread grooves, said movable pulley member being moved axially by driving said threaded shaft with said nut arranged so as to be not rotatable and not axially movable and said threaded shaft coupled to said movable pulley member so as to be rotatable and axially movable.
 2. A belt type infinite variable-speed drive as claimed in claim 1 wherein said ball circulating portions are within the outer periphery of said nut.
 3. A belt type infinite variable-speed drive as claimed in claim 1 or 2 wherein a plurality of said ball circulating portions are provided and wherein said ball circulating portions are arranged in an area where the load acting on said ball screw mechanism is small.
 4. A belt type infinite variable-speed drive as claimed in any of claims 1-3 wherein said threaded shaft is formed to be hollow and has its inner peripheral side rotatably coupled to said movable pulley member through a bearing.
 5. A belt type infinite variable-speed drive as claimed in any of claims 1-4 wherein a coupling member is fixed to one end of said threaded shaft, said coupling member comprising a flange extending outwardly beyond the outer periphery of said threaded shaft and an overhang overhanging along the outer periphery of said nut outwardly from said flange to form an annular space for receiving said nut between said overhang and the outer periphery of said threaded shaft, and a gear for transmitting a driving force to said threaded shaft is provided around said overhang.
 6. A belt type infinite variable-speed drive as claimed in claim 5 wherein said gear is formed integrally with said coupling member.
 7. A belt type infinite variable-speed drive as claimed in claim 5 or 6 wherein the overhanging length of said overhang is larger than the maximum stroke of the axial relative movement between said threaded shaft and said nut to cover the outer peripheral side of said annular space over the entire axial length.
 8. A belt type infinite variable-speed drive as claimed in claim 7 wherein a seal means for sealing said annular space between the inner periphery of said overhang and the outer periphery of said nut is provided.
 9. A belt type infinite variable-speed drive as claimed in claim 8 wherein said seal means sets the radial gap between the inner periphery of said overhang and the outer periphery of said nut at a minimum value.
 10. A belt type infinite variable-speed drive as claimed in claim 8 wherein said seal means comprises an elastic member mounted to the inner periphery of said overhang or the outer periphery of said nut to seal a radial gap therebetween. 